1. Field of the Invention
The present invention relates to a vertical alignment film and a VA mode liquid crystal cell.
2. Description of the Related Art
In the past, as a process for producing liquid crystal cells, a liquid crystal vacuum injection process has been adopted in which liquid crystals are injected due to the difference in pressure between the inside and outside of the panel. In recent years, however, now that a liquid crystal TV has become large-sized, a problem arises that the liquid crystal vacuum injection is time-consuming in the production.
To reduce the time for producing liquid crystal, a one drop filling (ODF) process has been developed. In the one drop filling process, a liquid crystal is dropped directly on a base panel, and the dropped liquid crystal is evenly distributed over the whole panel by a coalescing pressure of panels, and a liquid crystal layer is formed.
When a VA (vertical alignment) liquid crystal cell is produced according to the ODF process, it is known that the liquid crystal compound can be aligned vertically by disposing a polyimide-based alignment film containing a hydrophobic component such as a long chain alkyl group, a fluorine-substituted alkyl group and an alicyclic skeleton inside the pair of the panels between which the liquid crystal compound is put (see Japanese Patent Application Laid-Open (JP-A) Nos. 2007-256378 and 2007-225791).
However, since a liquid crystal compound is hardly compatible with the hydrophobic components in the alignment film, it has been problematic that the liquid crystal compound is difficult to be wetted and spread over, so that the alignment film is overloaded, and uneven alignment tends to occur.
Meanwhile, there has been developed another technique in which even when the polyimide-based alignment film contains only a small amount of hydrophobic components, a liquid crystal compound is easy to be wet and spread over and is aligned vertically by subjecting rubbing treatment to the polyimide-based alignment film.
However, such rubbing is likely to cause uneven rubbing corresponding to the surface roughness of the base panel; generation of static electricity due to the rubbing; and attachment of fine; and attachment of fine dusts; and thus makes it difficult to sufficiently align the liquid crystal compounds vertically. In a VA mode liquid crystal cell, such insufficient vertical alignment of the liquid crystal compounds often causes a light leakage when displaying black color in the liquid crystal display apparatus using the VA mode liquid crystal cells.
In order to produce a VA mode liquid crystal cell through the ODF method, a technique has been disclosed which utilizes a film on which a polymerizable liquid crystal compound is deposited in a hybrid aligned state as a vertical alignment film (e.g., JP-A No. 2000-122066).
However, even when the technique described in the JP-A-No. 2000-122066 is used, liquid crystal compounds cannot be fully aligned vertically, and the light leakage occurs when a black color is displayed.
Thus, a vertical alignment film still remains unsatisfactory which is capable of vertically aligning liquid crystal compounds sufficiently, without causing light leakage when black is displayed, and capable of being produced in a short time by an ODF process.